1. Field of the Invention
The present invention relates to a data transmission/reception apparatus for a Base Transceiver Station (BTS) in a mobile communication system, and more particularly to a data transmission/reception apparatus for a BTS system composed of a main system and a remote system.
2. Description of the Related Art
Typically, a mobile communication system is composed of a plurality of Base Station Controllers (BSCs) connected to a lower layer of a Mobile Switching Center (MSC) and a plurality of BTSs connected to a lower layer of the BSCs. The BTSs establish data transmission/reception with mobile terminals via RF channels. Since the BTSs are connected to the mobile terminals via RF channels, the signal transmission distance of the RF channel between the BTSs and the mobile terminals is an important factor when determining the cell areas of the BTSs. Another factor is the number of subscribers contained in one BTS, among a variety of factors to determine cell areas of the BTSs. Therefore, a cell area of the BTS of an urban district is different from that of a rural district. More specifically, a signal transmission distance is very short in the case where the buildings are closely situated together in a given area such as an urban district, resulting in a small cell area of the BTS in the urban district. Moreover, the number of subscribers in urban districts increases more and more, such that a cell area of the BTS becomes smaller and smaller. On the other hand, in the case where there are a small number of subscribers and few obstacles in a given area such as a rural district, a cell area of the BTS becomes wider.
However, in the case where the BTSs are installed by considering only a transmission distance of signals transmitted from the BTSs, even though there are few subscribers in a given area, there may be underutilization of BTS resources. Otherwise, in the case where a signal transmission distance from the BTSs becomes shorter because the channel environment is excessively deteriorated, even though there are a great number of subscribers in a given area, the BTS resources may be inefficiently used in light of the number of subscribers contained in each BTS. As described above, underutilization of BTS resources may occur due to a variety of environmental factors, such that it is necessary to solve this inefficiency.
To prevent the underutilization of the BTS resources, there has been proposed an architecture wherein a BTS system is divided into a main system and a remote system to increase its own cell area. A main system and a remote system of the BTS system will hereinafter be described with reference to FIGS. 1 and 2.
FIG. 1 is a view illustrating the coupling between a main system and a remote system of a BTS through a coaxial cable. Referring to FIG. 1, the BTS 100 includes a main system 111 and a plurality of remote systems 131-a to 131-n. The main system 111 is connected to the plurality of remote systems 131-a to 131-n through a coaxial cable 120, that is, the main system 111 is connected to more than one remote system. In the case of using the coaxial cable 120, the remote systems 131-a to 131-n are adapted to separate an RF block (e.g., an RF transceiver) from the main system 111. The remote systems 131-a to 131-n and the main system 111 are interconnected over the coaxial cable 120, such that the system configuration shown in FIG. 1 can be applicable to a conventional system without changing the internal configuration of the conventional system. However, the coaxial cable 120 is subject to significantly more signal leakage than an optical cable, such that there may also be leakage of data. Further, the distance between the main system 111 and the remote system 131-a, . . . , or 131-n is limited. Therefore, in order to solve the limitation in distance between the main system 111 and the remote system 131, there has been proposed another architecture for connecting such a main system with a remote system through an optical path, as shown in FIG. 2.
FIG. 2 is a view illustrating a block diagram of a system for connecting a main system and a remote system through an optical cable. With reference to FIG. 2, an optical cable 140 is adapted as a transmission path. The main system 110 includes a main module 111 and a Synchronous Digital Hierarchy (SDH) transmitter 115 interfaced with the optical cable 140. In more detail, the main system 110 performs the same function as in FIG. 1, but further includes a SDH transmitter 115. The remote system 130 includes a plurality of remote systems 130-a to 130-n. Each remote system 130-a, . . . , or 130-n includes a SDH transmitter 135-a, . . . , or 135-n and a remote module 131-a, . . . , or 131-n. The SDH transmitter 135 interfaces with data transmitted from the main system 110 via optical signals. The remote system 130 is the same as that of FIG. 1, but further includes a SDH transmitter 135.
The SDH transmitter 135 of the remote system 130 is identical with the SDH transmitter 115 of the main system 110. In the case of transmitting data over the SDH transmitters 115 and 135, the SDH transmitters 115 and 135 perform data conversion in the form of SDH, and modulate the converted data onto an optical signal. In the case of receiving data over the SDH transmitters 115 and 135, the SDH transmitters 115 and 135 convert the optical signal into an electric signal, demodulate the electric signal in the form of SDH, and transmit the demodulated signal to the main system 111 and remote module 131, respectively.
Referring to FIG. 2, the SDH transmitters 115 and 135 perform data conversion in the form of SDH, and either convert an optical signal into an electric signal or convert the electric signal into the optical signal, and thereby increase the data transmission distance and the cell area of the BTS. The BTS 100 should be in synchronization with all of the data at the same time, but it may not be actually so even though system synchronization is established among a plurality of remote modules. More specifically, in the case of transmitting data from the main system 110 to the remote system 130-a, . . . , or 130-n, it is necessary for the main system 110 to execute data transmission to the remote systems 130-a to 130-n at the same time. The BTS must execute a specified function such as a handover function because a plurality of mobile terminals of the BTS can freely move anywhere, such that a call transfer should also be completed at the same time that the handover function is executed. Therefore, in the case where any BTS does not effectively perform such a handover function, there may occur a loss of traffic data.
The data transmitted over the SDH transmitters is defined as the Synchronous Transfer Mode (STM-n) frame data. The aforementioned systems need to accurately detect individual positions of the STM-n frames in order to detect payload data. In more detail, in the case of using only the above SDH transmitters without any other applications, synchronization for executing a real handover among a plurality of systems may not be normally established even though synchronization condition is established among the systems. In addition, it is impossible for the STM-n frame data to restore data in either the main system 111 or the remote modules 131-a to 131-n. 